1. Field of the Invention
The present invention comprises a method and apparatus for performing operations in a well, such as wireline operations using a wireline lubricator assembly. More particularly, the present invention provides a method and apparatus for temporarily securing and sealing a vessel (such as a wireline lubricator) within a well in order to introduce and extract lengthy tool strings (such as wireline tools) to the well bore while encountering elevated wellbore pressures.
2. Brief Description of the Prior Art
During conventional drilling operations, a bore hole is drilled from the surface into the earth's crust through a wellhead assembly. A blowout preventer assembly is typically mounted to such wellhead assembly; such blowout preventer assembly usually includes an upper annular blowout preventer and one or more ram-type blowout preventers; when closed, said blowout preventers are designed to withstand fluid pressure from below. A bell nipple assembly is typically mounted to the upper annular blowout preventer of the blowout preventer assembly and extends upward toward the rig floor of a drilling rig or completion rig.
In most instances, said bell nipple assembly comprises a length of pipe having a relatively large diameter that extends from the uppermost extent of a blowout preventer assembly to a well opening at the drilling rig floor. The bell nipple typically serves as a “funnel” to guide drilling tools into and out of the upper opening of a well. Most conventional bell nipples also serve as conduits for drilling muds and/or other fluids present within a well.
Drill pipe or other tubular goods are usually inserted into a well and extend downwardly through the rotary drilling table, the bell nipple assembly, the blowout preventer assembly, the wellhead and downward into the well bore. Drilling mud or other fluids are usually introduced into the well through the drill pipe or other tubular goods to control reservoir pressures in the well. However, in the event that such reservoir pressure becomes excessive, the blowout preventers of the blowout preventer assembly may be actuated to seal off the upper opening of the well to control such excessive well pressures from below. For example, the annular blowout preventer may be closed around the outer surface of the drill pipe to seal off the annulus between the drill pipe and the surrounding casing or hole.
At certain times, particularly during completion of a well or during workover operations, a pipe string can be removed and various types of tools can be lowered into a well and suspended from a wireline or cable. Such wireline operations typically require the installation of a wireline lubricator assembly; on rigs and other installations without a permanent Christmas tree, the lubricator can be used, in conjunction with the blowout preventer assembly, to control pressure from below that may be encountered in a well while performing various wireline operations.
Generally, a lubricator assembly should be of sufficient size and length to totally contain the entire length and circumference of wireline tool or equipment being used. If desired (such as when well pressure is unexpectedly encountered while wireline operations are being performed) wireline tools can be retracted from the well bore up into the lubricator. Once the wireline tools are completely withdrawn inside the lubricator, the blind rams of the ram-type blowout preventers can be closed without contacting the wireline or any attached tools. The wireline tools and equipment can then be safely removed from the lubricator, the well pressure being contained below said blind rams.
One type of existing prior art wireline lubricator, frequently referred to as a “flange-type” lubricator, requires the removal of the entire bell nipple assembly prior to installation of such lubricator. Removal of a bell nipple frequently requires unbolting of many bolts from the flange connection between the bell nipple assembly and the blowout preventer assembly, as well as the connection between the flowline and the bell nipple assembly. Once the bell nipple assembly has been removed, the flange-type lubricator can be positioned on the uppermost end of the blowout preventer assembly and bolted thereto. The bolted connection between the lubricator and blowout preventer assembly must be able to withstand well pressure and requires testing for this purpose.
After wireline operations are completed, the flange-type lubricator assembly must then be unbolted and removed. Thereafter, the bell nipple assembly must be reattached to the blowout preventer assembly and the flowline must be reattached to the bell nipple assembly. Use of such flange-type lubricators can be very time consuming. The changing out of the bell nipple assembly and installation of the flange-type lubricator assembly may require several hours of rig time, which translates into costly rig rental charges.
Alternative lubricator devices have been developed in an effort to avoid the time and expense associated with conventional flange-type lubricators. In one embodiment, a lubricator assembly is inserted into the central bore of the blowout preventer assembly and bell nipple, and anchored in place using chains or other similar means. Although such chains or other anchoring means are arguably functional in applications involving low well pressures, this approach is not preferred when elevated well pressures are encountered.
Another alternative involves use of a spool member which is installed between the blowout preventer assembly and the bell nipple assembly. The spool has a plurality of locking pins radially movable between retracted positions (in which the pins to do not penetrate the spool bore), and extended positions (in which the pins penetrate the spool bore). A lubricator assembly includes a tubular mandrel which may be lowered and locked in the bore of the spool member in non-sealing engagement therewith by said locking pins. Unfortunately, as drilling operations encounter greater pressures, locking means having greater strength characteristics are required.
Existing methods for installing wireline lubricator assemblies suffer from a number of significant shortcomings. Thus, there is a need for an improved method and apparatus for quickly and efficiently locking a wireline lubricator assembly in place having greater strength characteristics than existing lubricator locking devices, and permitting operation in elevated pressures.